
theorem Th17:
  for L being LATTICE, x being set holds x is prime Filter of L
  iff x is prime Ideal of L opp
proof
  let L be LATTICE, x be set;
  L opp opp = the RelStr of L by LATTICE3:8;
  then x is prime Filter of L iff x is prime Filter of L opp opp by Th15;
  hence thesis by Th16;
end;
